Chevrolet/Geo Metro

Comments

I bought a '90 Turbo Firefly from a guy in Grande Prairie, AB and want to Atkinson cycle it. I'll get pistons machined for about a 45:1 compression ratio (with valve clearance pockets) then get an Atkinson Cycle cam ground such that the intake valves remain open past BDC sufficient to make the effective compression ratio about 6 1/2:1. Thus the compression ratio will be standard while the expansion ratio will be very large at 45:1, pulling the exhaust temperature way down and the thermal efficiency up considerably. Problems I'm concerned with will be that the exhaust enthalpy entering the turbine will be way down (considerably reduced temperature and pressure, thus degrading turbo performance. And the engine power density will fall way off, possibly down to 20 hp max or so, diving rise to drive ability problems. So we'll see. I any case, mpg should shoot way up.